CN1970680A - oil well fracturing agent - Google Patents

Abstract

The invention relates to an oil well fracturing agent, which comprises the following components in part by weight: a) a proppant; and b) a galactomannan having a molecular weight of about 100,000 daltons to about 250,000 daltons. The present invention also relates to a galactomannan produced by a process for depolymerizing galactomannan to a predetermined molecular weight, the process comprising the step of subjecting the galactomannan to radiation consisting essentially of electron beams.

Description

oil well fracturing agent

This application is a divisional application of the invention patent application 03817788.9 filed on June 24, 2003 with the title of "Method for Reducing the Molecular Weight of Polysaccharides with Electron Beam".

Cross References to Related Applications

This application claims the benefit under 35 U.S.C. § 119 of U.S. Provisional Application No. 60/391,320, filed June 25, 2002.

Field of the invention

The invention relates to an oil well fracturing agent.

Background technique

Polysaccharides, especially galactomannans such as guar and hydroxypropyl guar, as well as xanthan and xanthan gum, have a variety of uses. Guar gum, in its gum form, is primarily used in food and personal care products for its thickening properties. The gum has 5-8 times the thickening power of starch. Guar gum is also used as a fracking aid in oil extraction.

Guar gum is a slimy pulp found in the seeds of the leguminous plant Cyamopsis tetragonolobus. The seeds consist of a pair of tough, non-brittle endosperm parts, hereafter referred to as guarsplits. Guar watercress contains guar gum, but is tough and extremely difficult to grind into powder form for recovery of the gum. After processing, natural guar gum is obtained in the form of a yellow powder having a molecular weight of approximately 2,000,000 Daltons to 5,000,000 Daltons.

In certain applications of guar gum, such as in food and personal care compositions, in oil well fracturing and oil recovery, relatively low molecular weight materials are preferred for better performance. For example, in oil wells, when used as a fracturing aid, it is preferred that guar gum has a molecular weight of 100,000 Daltons to 250,000 Daltons because such low molecular weight gums are better obtained in oil recovery operations. High fracture conductivity and low formation damage results. Additionally, since guar gum used in oilfield applications will be modified with crosslinking additives as described below, the depolymerized guar gum must be capable of crosslinking.

Low molecular weight guar gum has been obtained by depolymerizing natural guar gum. One method currently used to depolymerize guar gum is by treatment with hydrogen peroxide. However, depolymerization by treatment with hydrogen peroxide has the disadvantage of being difficult to control to obtain guar gum in a predetermined molecular weight range. More specifically, hydrogen peroxide treatment typically produces depolymerized guar gums with a polydispersity of 3-5, which is too high. (Polydispersity is defined as the weight average molecular weight of the processed guar divided by the number average molecular weight.) Depolymerized guar for use in oil well production should have a polydispersity value of no greater than about 3.0. This depolymerization process also causes the guar gum to form agglomerates with hydrogen peroxide, which reduces the purity of the depolymerized guar gum.

US Patent No. 5,273,767 relates to a method of making modified rapidly hydrating xanthan gum and/or guar gum and sterilizing food products containing xanthan gum and/or guar gum by irradiation. The irradiation can be performed with a high energy electron beam at a level of about 0.1 to 4.5 Mrad.

US Patent No. 6,383,344 B1 discloses a method of reducing the molecular weight of polysaccharide polymers, especially hyaluronic acid and carboxymethylcellulose, by irradiating the polymers. Specific forms of irradiation disclosed are with gamma rays and microwaves. The preferred form disclosed is gamma radiation. However, the use of gamma radiation requires strict safety precautions because gamma radiation produced by radioactive sources is highly toxic.

The article titled "The effect of Gamma Irradiation on Guar Gum, Locust Bean Gum (Gum Tragacanth) and Gum Karaya" by King et al., FoodHydrocolloids, Volume VI, No.6, pages 559-569, 1993 reported the use of low-dose The gamma irradiation method of treating galactomannan, such as guar gum. The resulting product was disclosed to have low viscosity. The article states that the viscosity of solutions of guar and locust bean gums decreases with increasing gamma radiation dose when irradiated in dry powder form.

British Patent Publication No. 1,255,723 relates to the depolymerization of water-soluble cellulose ethers by irradiation with high energy electron beams. The method involves irradiating a layer of free-flowing particulate water-soluble cellulose ether having a uniform depth tuned to be within 10% of the penetration depth of the electron beam. Cellulose ethers are substituted polysaccharides, but not galactomannans. This patent does not disclose depolymerization of the polymers to form products having a predetermined molecular weight range or a polydispersity value below about 3.0.

According to US Patent No. 5,916,929, irradiation of polymeric materials results in two substantially different types of products. Certain polymers such as polyethylene and its copolymers, polybutadiene, polyvinyl chloride, natural rubber, polyamides, polycarbonamides and polyesters undergo molecular bonding and eventually crosslinking. Crosslinking substantially increases the molecular weight of the polymer and increases its melt viscosity (measured by melt flow rate), ie the value of the melt flow rate decreases. A second class of polymers such as polypropylene, polyvinylidene chloride and fluorocarbon polymers (including polytetrafluoroethylene) are known to undergo polymer degradation when irradiated with high energy ionizing radiation. This chain scission tends to reduce the molecular weight of the polymer, which is reflected in a decrease in the melt viscosity property as measured by an increase in melt flow rate (MFR).

Summary of the invention

The object of the present invention is to depolymerize polysaccharides, especially galactomannans, such as guar gum and xanthan gum, to form products with predetermined low molecular weights falling within a very narrow molecular weight range.

Another object of the present invention is to depolymerize guar splits to a predetermined molecular weight, thereby facilitating the use of guar splits and the recovery of guar gum from guar splits.

Yet another object of the present invention is to provide a process for depolymerizing polysaccharides, especially guar gum, with reduced levels of impurities in the final product.

Yet another object of the present invention is to provide a method for the depolymerization of polysaccharides which can be carried out at about room temperature without the need to use radioactive materials as sources of radiation for depolymerization.

Yet another object of the present invention is to produce depolymerized galactomannan and xanthan gums having a predetermined molecular weight and a polydispersity below about 3.0 and undergoing rapid hydration.

These and other objects can be achieved by the method of the present invention wherein polysaccharide polymers, especially xanthans and galactomannans such as guar gum, xanthan gum, guar split, water-swellable guar split and hydroxypropyl Guar flour is deagglomerated by irradiation with high-energy electron beams. According to the present invention, guar gum having a molecular weight of at least 2,000,000 Daltons is depolymerized to a lower predetermined molecular weight. These depolymerization products can be used in food applications, cosmetics, pharmaceuticals and other industrial applications such as flowable insecticides, liquid feed additives, detergents, ceramics and coatings. In a preferred embodiment, depolymerization is performed to produce guar gum having a molecular weight of less than about 700,000 Daltons. In a more preferred embodiment, depolymerization is performed to form galactomannan having a molecular weight of less than about 500,000 Daltons. In an especially preferred embodiment, depolymerization is performed to form galactomannans having a molecular weight of less than about 300,000 Daltons. In the most preferred embodiment, depolymerization is performed to form galactomannans having a molecular weight of about 100,000 Daltons to about 250,000 Daltons and a polydispersity of less than about 3.0 Daltons, wherein at least 90% Becomes hydrated in 3 minutes. The method of the invention is also applicable to the depolymerization of other galactomannans. Also within the scope of the present invention are depolymerized products, especially guar and substituted guars, produced according to the methods described herein, most preferably having the predetermined molecular weights mentioned above, as well as molecular weight ranges and multiples below about 3.0. dispersible, and at least 90% hydrated product within 3 minutes. These depolymerization products are especially useful as fracturing agents in oil recovery.

The type and dosage of high energy electron beams used in the practice of this invention will vary depending on the type of polysaccharide polymer being treated, the degree of molecular weight reduction desired and the desired rate of depolymerization. The dose of electron beam radiation to which the guar gum is exposed for depolymerization of the guar gum is preferably from about 1 Mrad to about 15 Mrad, although lower and higher doses of electron beam radiation than this preferred range can also be used.

Brief description of the drawings

Figure 1 is a graph showing the decrease in the molecular weight of guar gums obtained from guar split, Jaguar 6003VT and Jaguar 8000 guar gums with increasing radiation dose from exposure to high energy electron beams.

Figure 2 is a graph showing the molecular weight of guar gum obtained from high energy electron beam irradiated guar gum powder, guar watercress, and hydroxypropyl guar gum.

Figure 3 is a graph showing the relative solubility in water of materials obtained from guar powder or hydroxypropyl guar gum increases with increasing radiation dose to exposure.

Figure 4 is a graph showing the weight average and number average molecular weight reduction of guar gum obtained from Agent AT-2001 guar gum comprising hydroxypropyl guar gum and a small amount of sodium hydroxide.

Figure 5 is a graph showing the effect of sample thickness on the number and weight average molecular weight of depolymerized guar gum.

Figure 6 is a graph showing the effect of sample thickness on the polydispersity of irradiated guar gum.

Detailed description of the invention

A. Polysaccharide

The term "polysaccharide" as used herein refers to polymers with repeating sugar units, including starch, polydextrin, lignocellulose, cellulose and their derivatives (e.g. methylcellulose, ethylcellulose, carboxy Methylcellulose, hydroxyethylcellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, starch and amylase derivatives, pullulan and its derivatives and other chemical and physical modified starch) and so on.

B. Galactomannan

Galactomannans are polysaccharides mainly composed of the monosaccharides mannose and galactose. Depending on the plant of origin, the mannose units form hundreds of (1→4)-β-D-mannopyranosyl residues with 1→6 linked α-D-galactopyranosyl residues separated by different distances. A chain of base residues. The galactomannans of the invention can be obtained from a number of sources. Such sources include guar gum, guar split, cationic and nonionic guar gum, locust bean gum and tara gum as further described below. In addition, galactomannan can also be obtained by typical synthetic routes or can be obtained by chemical modification of naturally occurring galactomannan.

1. Guar gum

Guar gum, often referred to as "guar powder" after grinding, refers to the slimy pulp found in the seeds of the legume Cyamopsis tetragonolobus. The water-soluble part (85%) is called "guaran", which consists of (1→4)-β-D-mannopyranosyl units linked by (1→6) bonds with α-D-galactopyranose A linear chain of basic units. The ratio of D-galactose to D-mannose in guaran is about 1:2. Guar gum can be in the form of a whitish powder that is dispersible in hot or cold water. Guar gum is available, for example, from Rhodia Inc. (Cranbury, New Jersey), Hercules, Inc. (Wilmington, Delaware) and TIC Gum, Inc. (Belcamp, Maryland).

2. Guar watercress

Guar seeds consist of a pair of tough, non-brittle endosperm parts, hereinafter referred to as "guar splits", between which a brittle germ (germ) is sandwiched. After dehulling, the seeds are split, the embryos (43-47% of the seeds) are removed by sieving, and the petals are ground again. Guar gum is present in the flap in a form contained in tiny cells with water-insoluble cell walls. Guar gum in these cells disperses rather slowly in water, so it is necessary to break down the cell walls and obtain a fine particle size.

Petals are reported to contain approximately 78-82% galactomannan polysaccharides and small amounts of certain proteinaceous material, inorganic salts, water insoluble gums and cell membranes, and some residual testa and germ. They are tough and extremely difficult to grind.

3. Locust bean gum

Locust bean gum or carob gum is the refined endosperm of the seeds of the carob tree ceratonia siliqua. The ratio of galactose to mannose in these gums is about 1:4. The cultivation of the carob tree is ancient and well known in the field of gum production. Such gums are commercially available from TIC Gum, Inc. (Bekamp, Maryland) and Rhodia, Inc. (Cranbury, New Jersey).

4. Tara gum

Tara gum is obtained from the extracted seed gum of the tara tree. The ratio of galactose to mannose is about 1:3. Tara gum is not produced industrially in the United States, but the gum is available from various sources outside the United States.

C. Modified galactomannan

Other galactomannans of value are modified galactomannans, including carboxymethyl guar, carboxymethylhydroxypropyl guar, cationic hydroxypropyl guar, hydroxyalkyl guar , including hydroxyethyl guar, hydroxypropyl guar, hydroxybutyl guar and higher hydroxyalkyl guars, carboxyalkyl guars, including carboxymethyl guar, carboxypropyl guar Guar gum, carboxybutyl guar gum, and higher alkylcarboxy guar gum, hydroxyethylated, hydroxypropylated and carboxymethylated derivatives of Guaran, hydroxyethylated and carboxymethylated derivatives of Carubin substances, hydroxypropylated and carboxymethylated derivatives of Cassia-Gum and modified galactomannan or galactomannan gums. A preferred modified galactomannan is hydroxypropyl guar gum with low molecular substitution, eg less than 0.6.

D. Xanthan

Valuable xanthans are xanthan gum and xanthan gel. Xanthan gum is a polysaccharide gum produced by Xathomonas campestris. Xanthan gum contains D-glucose, D-mannose, D-glucuronic acid as the main hexose units, also contains pyruvate, and is partially acetylated.

According to the present invention, polysaccharide polymers, especially galactomannans, such as solid guar gum, and xanthans such as xanthan gum are irradiated with a high energy electron beam. Irradiation caused depolymerization of the polymer to a controlled low molecular weight. The amount and time of such irradiation used depends on the particular material being treated. The type and amount of radiation employed may vary for the particular polymeric material processed in accordance with the present invention. The method of the invention is applicable to a wide variety of polysaccharides, but is particularly applicable to galactomannans and modified galactomannans. The method is especially useful for the depolymerization of guar gum or its derivatives, such as hydroxypropyl guar gum, in powder or loaf form.

The polymers treated according to the invention are in the solid state before and during treatment. The term "solid state" includes powders, pellets, flakes, particles and the like. Irradiation is applied directly to the solid polymer, preferably as the polymer is conveyed on trays on the drive belt of the production line. According to the invention, the solid polymer to be depolymerized is placed on the tray to a thickness that facilitates penetration of the solid material by the high-energy electron beam. Polydispersity can be controlled by adjusting the thickness of the material. If all material is penetrated by the electron beam, the polydispersity is reduced. The layer of solid material to be depolymerized should have a substantially uniform thickness in order to obtain good polydispersity values for the depolymerized product. For safety reasons, the polymer to be treated can be covered with a radiolucent plastic film. The trays are then transported on a conveyor belt into the radiation chamber. The polymer is irradiated with a high-energy electron beam at a defined dose rate, depending on the desired degree of depolymerization of the polymer. In irradiation processing, dose is defined as the energy absorbed by the target material. Doses are defined in units of gray or megarads. 1 kilogray equals 1,000 joules/kg. 1 Mrad equals 1,000,000 ergs/gram. Therefore, 1 megarad equals 10 kilograys. A preferred dose is about 1 to about 15 Mrad or about 10 to about 150 kilograys (kGy), which can be produced by a 4.5 MeV generator operating at 15 mA. Such generators are commercially available from E-Beam Services, Inc. of Plainview, New York.

Dose rate is the amount of time required to deliver the radiation dose required to depolymerize a polymer to a predetermined molecular weight. This rate has a direct effect on how long it takes to deliver a given dose, and thus the amount of time the polymer is exposed to ionizing radiation. The high-power beam produces the irradiation dose rapidly. As shown in Table 1, even at low power (1 kW), the electron beam delivers the target irradiation dose 40 times faster than its equivalent gamma irradiation. The use of high power beams allows for higher production rates of depolymerized guar gum.

Table 1. Comparison of irradiation doses by gamma irradiation method and electron beam irradiation method

Gamma irradiation method Electron beam irradiation method target dose dose rate (method specific) time required to deliver dose 20kGy10kGy/hr2hr(120min) 20kGy400kGy/hr0.05hr(3min)

High power beam irradiation of polymers is preferably performed at room temperature, and can be performed at higher and lower temperatures.

A high voltage electron beam generator producing a dose of 1-10 MeV is preferred because it can penetrate deeply into the material, allowing thicker layers of material to be irradiated. >10 MeV can be used, but this is not preferred as it can generate radioactivity from high atomic number elements. High voltage electron beam generators are available from Electron Solutions Inc. and Science Research Laboratory, Somerville, Massachusetts, Ion Beam Applications, Louvain-Ia-Neuve, Belgium and The Titan Corporation, San Diego, California.

Low voltage electron beam generators (150keV-1MeV) are also preferred. The material is irradiated as a layer as it passes; optionally, the irradiating occurs after the material has been mechanically ground into a powder. Such generators are generally less expensive and do not require a concrete shield. Low voltage electron beam generators are available from Energy Sciences, Inc., Wilmington, Massachusetts (EZCure), Radiation Dynamics Inc., Edgewood, New York (Easy E-beam), and Electron Solutions Inc., Somerville, Massachusetts (EB-ATP) . This equipment is usually mainly used for surface radiation curing.

As mentioned above, the degree of depolymerization is influenced by the molecular weight of the initial polymer to be treated and the predetermined molecular weight of the depolymerized product. Guar gum has a molecular weight in excess of 2,000,000 Daltons and typically 2,000,000-5,000,000 Daltons. In a preferred embodiment of the invention, the polymer is depolymerized to less than about 700,000 daltons, more preferably less than about 500,000 daltons, still more preferably less than about 300,000 daltons, most preferably about 100,000 daltons Daltons to 250,000 Daltons. By utilizing the present invention, galactomannan polymers can be depolymerized into products having molecular weights lower than those mentioned above, most preferably from about 100,000 Daltons to about 250,000 Daltons.

As described in detail below, the depolymerized galactomannan changed to a state of more than 90% hydration within 3 minutes.

As mentioned above, depolymerized guar gum can be used to facilitate oil recovery. The productivity of oil and gas wells can be increased by hydraulically fracturing and opening up oil or gas zones. Hydroxypropyl guar gum solutions and similar gelling agents are used in this method, which is known as hydraulic fracturing. In the practice of this method, a highly viscous liquid fracturing fluid carrying proppants such as sand is pumped into an oil or gas-bearing formation at extremely high pressures, thus forming fractures in the formation. When the hydraulic pressure is released, the proppant keeps the fracture open. Oil and gas are then recovered at an increased rate.

Galactomannans, such as guar gum or hydroxypropyl guar gum, are added to fracturing fluids to increase their viscosity and proppant delivery capabilities. Additionally, in the case of guar gum and guar watercress, hydroxypropyl guar gum, etc., viscosity and proppant transport capabilities can be increased even further through the use of crosslinking additives. Some known crosslinking additives include borate esters as described in US Patent No. 3,974,077, and titanate or zirconate organometallic crosslinkers as described in US Patent Nos. 4,657,080 and 4,686,052, respectively. However, it has been found that excessively viscous fracturing fluids can fill fractures thereby hindering the rate of oil or gas recovery. This problem is alleviated by the method of reducing the viscosity of the fracturing fluid by replacing natural guar gum with depolymerized guar gum prepared according to the present invention.

As mentioned above, depolymerized galactomannan, xanthan and xanthan gum can be used in food applications, cosmetics, pharmaceuticals and other industrial applications such as flowable pesticides, liquid feed additives, detergents, ceramics and coatings. More specifically, the depolymerized guar gum can be used in a variety of food products, including sweets, processed fruits and vegetables, beverages, sauces and dressings, to provide consistency. The depolymerized galactomannan can also be used to provide consistency to household products, cheese, soup and pet food, as well as to provide body and pre-water binding to meat products.

The following examples of the invention are provided for illustrative purposes only. They are in no way intended to limit the invention.

Example 1

The following is the depolymerization of guar gum, guar watercress and guar gum derivatives by high energy electron beam irradiation

Example.

Guar watercress, guar gum in powdered form or hydroxypropyl guar gum in powdered form are placed in a container and covered with a very thin plastic film. The sample was irradiated with an electron beam generated by a 4.5 MeV generator operating at a beam current of 15 mA directed at the top surface of the tray. The doses used were 1 Mrad, 3 Mrad, 5 Mrad, 10 Mrad and 15 Mrad.

After irradiation, gel permeation chromatography (column, Supelco Progel-TSKG3000PW _XL and G6000PW _XL in series; mobile phase, 55 mM Na ₂ SO ₄ , 0.02% NaN ₃ ; flow rate, 0.6 ml/min; detector, Waters 410 Refractive Index; injection volume, 200 μl; temperature, 40° C.) analyzed the molecular weight of the treated samples. The sample was dissolved in the mobile phase to obtain a 0.025 wt% solution. Calibration curves were developed using stachyose and two guar gum samples with molecular weights of 667, 58,000 and 2,000,000 Daltons. The results obtained are shown in Table 2.

[0049] The decrease in molecular weight with irradiation dose was clearly demonstrated for three different types of samples (FIG. 1). The degree of depolymerization increased with the increase of irradiation dose. The degree of depolymerization was similar among the different materials treated and no significant changes were found for guar powder, guar flap or hydroxypropyl guar powder. The degree of disaggregation or molecular weight can be dose-dependent (Figure 1), so molecular weight reduction for a given dose can be easily predicted as long as the initial molecular weight is known prior to irradiation.

Table 2. Molecular weight distribution of irradiated guar gum

samples Peak Mp   Weight average molecular weight Mw Number average molecular weight Mn Polydispersity Mw/Mn Hydroxypropyl Guar Gum Powder, 1M rad Hydroxypropyl Guar Gum Powder, 3M rad Hydroxypropyl Guar Gum Powder, 5M rad Hydroxypropyl Guar Gum Powder, 10M rad Hydroxypropyl Guar Gum, 15M rad Guar Gum Guar gum powder, 0rad guar gum powder, 1M rad guar gum powder, 3M rad guar gum powder, 5M rad guar gum powder, 10M rad guar gum powder, 15M rad guar watercress, 1M rad guar watercress, 3M rad guar watercress, 5M rad guar watercress, 10M rad guar watercress, 15M rad 417,000173,000117,00064,70043,5002,960,000474,000196,000110,00059,90039,900588,000241,000120,00084,90047,200 513,000227,000141,00077,50053,8002,860,000571,000249,000132,00068,10046,400706,000314,000140,00094,20058,000 149,00067,00043,00025,20017,4001,200,000161,00078,90041,80021,70014,900224,000118,00049,00035,00019,400 3.443.353.283.073.082.373.543.163.163.133.113.162.662.832.692.99

Example 2

The following are examples of depolymerization of various guar types using low energy beams.

At Energy Science Incorporation, guar gum flaps (DPS), guar gum powder (Jaguar 6003VT) and hydroxypropyl guar gum (HPG, Jaguar 8000) were irradiated with a 200keV electron beam at 10 Mrad. The molecular weight was measured in the same manner as above. Not surprisingly, the powder forms of Jaguar 6003VT and 8000 were deagglomerated and found to have little effect on the flap. See Table 3. Compared to high-energy electron beams, the absorbed dose is greatly reduced due to the limited penetration of electron beam irradiation. The powder samples of Jaguar 6003VT and 8000 did receive some dose and were deagglomerated as the powder was placed in very thin layers. However, a relatively high polydispersity (3-4) of the depolymerized products was found compared to high energy electron beams, where the polydispersity of the polymerized products is typically 2-3. On the other hand, the penetration depth of the lobe was too small to cause any detectable depolymerization of the lobe. At least half of the energy was dissipated by the plastic wrap, although a surface dose of 10 Mrad was provided by the system. These results show that deaggregation is possible under the low energy electron beam, provided the material is properly fed under the electron beam at the proper thickness/density.

Table 3. Guar gum is depolymerized with a dose of 10 Mrad under low energy beam

sample Peak MWMp Weight average molecular weight Mw Number average molecular weight Mn Polydispersity Mw/Mn Guar WatercressJaguar 6003VTJaguar 8000 1,600,000171,000166,000 1,310,000231,000301,000 311,00069,90065,200 4.203.314.62

Example 3

In this example, depolymerization of guar gum and guar split was performed to provide an effective oil well fracturing fluid.

Several different types of guar gum and guar gum derivatives, namely guar watercress, Jaguar8000 (HPG) and Agent AT-2001 base were selected and depolymerized. (Agent AT-2001 Base is a popular guar-containing product used in oilfield applications, usually depolymerized by hydrogen peroxide, prior to depolymerization.) According to the Material Safety Data Sheet for Agent AT-2001 Base, Agent AT-2001 The base contains more than 85% 2-hydroxypropyl ether guar gum, less than 3% sodium hydroxide and the remainder water. These samples were packaged in plastic bags with a thickness smaller than the effective thickness of the electron beam and then irradiated with a dose of 3.8 Mrad using a 4.5 MeV 3-electron beam generator. The samples were then analyzed for molecular weight several days after irradiation. The results obtained are shown in Table 4.

All samples of guar split, Jaguar 8000 and Agent AT-2001 base were successfully depolymerized to the desired range. No differences were found between 4 identical samples of Agent AT-2001 base and between 2 identical samples of guar split. Reproducibility was found to be excellent. All depolymerized guar gums or their derivatives were found to have good polydispersity (<3) values compared to current _{H2O2 depolymerized} guar gums. Typical polydispersities found so far for this chemistry are 3-5. However, each product has a slightly different molecular weight, which can be easily adjusted to the target value by adjusting the radiation level. This may be attributed to the difference in the composition of the starting products of guar watercress, Jaguar 8000 and Agent AT-2001 base.

Table 4. Reproducibility of electron beam depolymerization

samples Peak MWMp Weight average molecular weight Mw Number average molecular weight Mn Polydispersity Mw/Mn Agent AT-2001 Alkali: #1#2#3#4 Mean % Standard Deviation (n-1) Jaguar 8000Agent AT-2001 Alkali-Water Swellable Clam Guar Bean Bean #1 Guar Bean Bean Bean #2 118,000116,000113,000114,000115,2501.9138,000100,000185,000194,000 136,000133,000132,000130,000132,7501.9185,000117,000238,000264,000 52,80054,60051,60052,70052,9252.368,70049,00094,50099,200 2.572.432.562.482.512.72.692.392.522.66

Example 4

In this example, the cross-linking ability of Agent AT-2001 base was investigated.

The viscosities of separate solutions of Agent AT-2001 base and Jaguar 8000 in distilled water were measured and found to be within the expected range based on molecular weight.

2.5% Agent AT-2001 base, 3.8Mrad: 14.5cP, at 511/sec and 75,

2.5% Jaguar 8000, 3.8 Mrad: 40cP at 511/sec and 75°F.

Agent AT-2001 base is currently available in cross-linked form for oilfield applications. It is important to ensure that the e-beam irradiated Agent AT-2001 base is also capable of crosslinking. This test is also helpful in determining whether there are any significant functional group changes accompanying depolymerization by irradiation. Therefore, a 2.5% solution of Agent AT-2001 base depolymerized by AgentAT-2001 base by irradiation was mixed with borax crosslinker and NaOH to increase the pH. Within seconds, the polymer solution turned into a gel. This experiment demonstrates that e-beam irradiated Agent AT-2001 base can be crosslinked with borax crosslinker.

Example 5-7

Examples 5-7 describe the pilot scale depolymerization of Agent AT-2001 base.

The pilot test was conducted at IBA's pilot plant in Long Island, New York. The samples were placed as a thin layer in a 19 x 19 x 5 cm plastic tray and covered with a plastic lid. Determines the depth of a material based on weight, density and area. The tray is then irradiated on the movable table. Vary surface dose, electron energy, and sample thickness. Material obtained from different batches of Agent AT-2001 base was also examined.

Color intensification with dose was observed for all samples treated and radiation shadowing was found on at least one side of each tray. Viscosity above 90% (maximum) was obtained within 3 minutes and it plateaued within 10-15 minutes. According to this definition, 100% is defined as complete hydration. Measure the viscosity of the irradiated material and follow the procedure described in the previous section. This viscosity is used as a surrogate for analyzing the degree of disaggregation. Only selected samples were subjected to molecular weight determination by gel permeation chromatography.

The degree of depolymerization of the irradiated Agent AT-2001 base was detected by measuring the viscosity immediately (within 2 hours) and several days after irradiation. Data were collected after the polymer was fully hydrated in water. The results showed that depolymerization continued after the cessation of irradiation (see Table 5). This phenomenon is common to all irradiations performed in the solid state, since the active species can be easily trapped in the lattice of the irradiated material. These substances cause further reactions and can last from seconds to days—even years—depending on temperature, solvent content, and the material itself. Further examination of this phenomenon for AgentAT-2001 base is described below.

Table 5. Viscosity reduction with time migration after irradiation

Energy (MeV) Dose (Mrad) Thickness (cm) 1.230.36 1.240.36 1.250.36 1.260.36 1.270.36 1.280.36 1.260.20 361.52 351.52 341.53 viscosity viscosity viscosity 1053435 662829 463132 263232 241213 181111 261314 191424 232021 332626

Example 5 concerns the effect of different irradiation doses on depolymerization of polymers.

A sample of Agent AT-2001 base was placed on the tray at a thickness corresponding to the effective thickness for the specified electron energy. Irradiation was performed with various doses and at three different energy levels, 1.2 MeV (with 0.2 MeV for energy loss due to packaging), 1.5 and 3.0 MeV. For 1.2 MeV, a 90 g sample was spread in a tray (3.6 mm thick, d=0.7) and then irradiated incrementally starting from 1 Mrad to obtain various doses. For 1.5 MeV, each experiment used a 160 g sample (6.4 mm, d=0.7), which was given an initial dose of 4 Mrad and then incrementally irradiated in 1 Mrad increments to obtain 5, 6 and 7 Mrad. All irradiations performed at 3.0 MeV used one shot. Viscosity was measured with a Fann 35 viscometer from Baroid, Houston, TX at 300 rpm with 2.5% actives, while the assumed humidity was assumed to be -10% (see Table 6). For application testing, a target viscosity of 23-28 cps was determined.

Table 6, Depolymerization of Agent AT-2001 base

dosage Viscosity (cps) (Mrad)12345678   1.2MeV/0.36cm380096352932101311 1.5MeV/0.64cm---36342722- 3.0MeV/1.52cm---262114--

The results clearly show that the polymer is depolymerized. For all three levels of electron energy, the viscosity decreased with increasing dose. Molecular weights of selected samples were determined by GPC and are shown in Table 7 and plotted in FIG. 4 . A very good MW-dose (D, Mrad) correlation was found for both weight-average (Mw) and number-average (Mn) molecular weights:

Log(Mw)＝5.6906-0.7881 log(D), correlation coefficient＝-0.9979

Log(Mw)＝5.2894-0.7176 log(D), correlation coefficient＝-0.9987

The polydispersity of these samples was 2.1-2.6 (see Table 7), better than those previously found. These desirable polydispersity values can be achieved with more uniform thickness and less material being irradiated beyond the effective thickness. The thickness effect is discussed below.

Experience has shown that with lower electron energies, slightly higher surface doses are required. This can be attributed to the energy loss of the electrons before they enter the material and the variation of the depth-dose distribution for different electron energies. The latter determines the cumulative dose or energy delivered by the electrons.

Table 7, the depolymerization of Agent AT-2001 base with various doses

Dose (Mrad)/Energy (MeV) Viscosity cP Peak MWMp   Weight average molecular weight Mw Number average molecular weight Mn Polydispersity Mw/Mn 1/1.23/1.26/1.27/1.24/3.05/3.0 3,8003519132621 368,000163,000116,000101,000129,000115,000 504,000194,000119,000110,000150,000153,000 195,00087,50056,20046,60060,00060,000 2.592.222.122.372.462.55

Example 6 concerns the effect of sample thickness of irradiated material (Agent AT-2001 base) on molecular weight and polydispersity.

Irradiation was performed with an electron energy of 1.2 MeV at a dose of 6 Mrad. Various amounts of sample are spread out on the inside of the tray. After irradiation, samples were cooled for at least 1 day prior to analysis. Viscosity and molecular weight were collected in the same manner as above (see Table 8). In order to obtain narrow polydispersity, irradiation must be performed within the effective thickness to ensure a more uniform dose distribution along the path (effective thickness of guar = 0.36 cm or 0.25 g/cm ² at 1.0 MeV). The effect of sample thickness on molecular weight and polydispersity, respectively, is clearly shown in Figures 5 and 6 . Molecular weight and polydispersity remain nearly constant throughout the effective thickness. They increase exponentially above the effective thickness as the sample size increases. Effective thickness varies with beam energy (MeV).

Table 8. Depolymerization of Agent AT-2001 base with various sample thicknesses*

Dose (Mrad) Viscosity cP Peak MWMp Weight average molecular weight Mw Number average molecular weight Mn Polydispersity Mw/Mn 0.120.280.360.520.71 141519362,500 116,000116,000122,000126,000135,000 111,000119,000125,000210,000467,000 50,40056,20056,60066,70089,100 2.202.122.213.155.24

*Irradiated with 6Mrad surface dose at 1.2MeV

Example 7 relates to the effect of using different batches of Agent AT-2001 base.

Agent AT-2001 base is produced from guar gum by hydroxypropylation in the presence of sodium hydroxide. The nature of the guar gum and the hydroxypropylation treatment itself often caused differences between different batches of AgentAT-2001 base. It is known that these differences can alter its reactivity with hydrogen peroxide, thus leading to different levels of depolymerization. However, as demonstrated in Example 1 above, the irradiation method of the present invention depolymerizes guar, guar powder, and hydroxypropyl guar to predetermined molecular weights. Therefore, differences in different batches of Agent AT-2001 base are not expected to cause any observable differences in the degree of disaggregation obtained under irradiation. For verification, four different batches of Agent AT-2001 base were irradiated at 5 Mrad in the effective thickness, and the solution viscosity was measured as described above. The samples were not covered with a plastic sheet. At an e-beam power of 2.2 MeV, with a sample thickness of 0.76-1.27 cm (below an effective thickness of 1.52 cm), the variance in sample thickness was minimized in order to evaluate the variance among batches. As shown in Table 9, the irradiated samples achieved viscosities of 11-15 cP, well within experimental error. The average viscosity was 13.4 cP and the standard deviation (n-1) was 1.13. No abnormal deaggregation upon irradiation in different batches was found.

Table 9. Depolymerization of different batches of Agent AT-2001 base*

Batch# Weight, g Thickness, cm Viscosity, cP ^25.29 H0210-997AH0210-071CRH0210-071ARH0210-997HR1H0210-071DRH0210997HRH0210997HRH0210997HR 317297.1297284.4269.8270320190 1.271.191.191.141.081.081.280.76  12.814.41512.613.61413.611.4

*Irradiated at 2.2MeV

Example 8-12

Examples 8-12 relate to the depolymerization of Agent AT-2001 base during production trial.

In these examples, irradiation was performed at 2.2 MeV in IBA's Gaithersburg production facility. Based on previously obtained data, a dosage of 4 Mrad and a charge of 0.79 g/cm ² , ie 14 lb/tray (8000 cm ² ), were the target parameters in order to produce a product with a molecular weight of approximately 200,000 Daltons. The amount of material loaded in the tray corresponds to the effective thickness of the electron beam. Verify radiation dose, thickness and lot size. The results of the tests performed here are listed in Table 10. Samples were weighed onto trays, spread and leveled by hand. There is a more pronounced difference in thickness because no mechanical leveling was used. Samples were taken from all trials. Viscosity was measured with a Fann 35 after dissolving 5.55 g of irradiated material with 1.5 g sodium monophosphate in water at room temperature. The results are given in Table 9.

Table 10

test# Dose, Mrad Lb/tray batch# 12345678 34544446  14141416.511.5141414 H0303221ARH0303221ARH0303221ARH0303221ARH0303221ARH0303192CRH0212269KRH0303221AR

Example 8 relates to viscosity measurements over time of the depolymerized Agent AT-2001 base produced in the assay.

Samples for Run 2 (tray #17, 4 Mrad, 14 lb/tray, lot H0303221AR) were taken approximately 15 minutes after irradiation. Viscosity was measured thereafter and then after 1.5 hr and 1 day (see Table 11). The viscosity of all samples of this test was also measured 20-90 minutes and 1 day after irradiation (see Table 12). Some samples showed significant viscosity differences between measurements taken immediately (20-90 minutes after irradiation) and 1 day later. This difference could be attributed to the rapid drop immediately after irradiation, since the time between irradiation and viscosity measurement was different for each sample. Table 12 clearly shows the rapid decline over this period. This result indicates that at least 1 hour is required before the viscosity stabilizes after irradiation. In the following examples, the viscosity after 1 day in which no further decrease was found was used for comparison.

Table 11. Viscosity change over time

Time (h) Viscosity (cP) 0.251.524 473529

In Example 9, a sample of the product produced in Experiment 2 described above was tested for AgentAT-2001 base uniformity.

In Trial 2 (4 Mrad, 14 lb/tray, lot H0303221AR), three samples were taken from different locations in a single tray and three other samples were taken from different trays. There were clear differences within a tray and between trays (see Table 12). Assuming that the viscosity of the material was completely stable after 1 day, the average for the three samples in one tray was 34.6±12.1 and the average for the six samples in four different trays was 33.9±12.0. These differences are most likely caused by differences in thickness, which will be described in the next example.

Table 12. Viscosity of samples

Test#Lot#Dosage (Mrad)Wt(lb)Tray Thickness(cm)Tray#Sample Viscosity ¹ Viscosity ² Viscosity ³ 1A3141.13724445 2A4141.13A231718 2A4141.133B342626.6 2A4141.13C464343.6 2A4141.135443738 2A41.137472930 2A41.138444547 4A41.33444041 5A40.93262426 6B41.13242223 7C41.13373334 3A51.13342729 8A5141.13181920

¹ Viscosity was measured within 2 hours of irradiation with a hydration time of 3 minutes.

² Viscosity was measured over 1 day with a hydration time of 3 minutes.

³ Viscosity was measured over 1 day with a hydration time of 15 minutes.

In Example 10, the effect of the thickness of the irradiated material was evaluated in terms of product viscosity.

Trials 4 and 5 were intentionally irradiated at 4 Mrad with 20% more and 20% less material respectively on the tray (lot H0303221AR). This trend is clearly seen when compared to the mean values of Trial 2 (see Table 13). Because the tray is not sufficiently leveled, there is a high probability of irradiation outside the effective thickness, ie at less than 20% of the effective thickness. The viscosities given here are just average values.

Table 13. Thickness effect

test# 4 2 (average) 5 Wt (lg) tray thickness (cm) viscosity ¹ viscosity ² viscosity ³ 16.51.33444041 141.13403334 11.50.93262426

^1See Table 12.

^2See Table 12.

³ See Table 12.

In Example 11, the effect of irradiation dose on product viscosity was evaluated.

The sample batch (H0303221AR) was irradiated in trials 1, 2, 3 and 8 at 3, 4, 5 and 6 Mrad respectively. As the dosage is increased, viscosity is expected to decrease. This trend is clearly seen when compared to the mean value of Trial 2 (see Table 14).

Table 14. Dose effect

Test #1 2 (average) 3 8 Dose (Mrad) 3 Viscosity ¹ 72 Viscosity ² 44 Viscosity ³ 45 4403334 5342729 6181920

^1See Table 12.

^2See Table 12.

³ See Table 12.

In Example 12, the effect of using different batches of Agent AT-2001 base was evaluated.

These different batches of 0303221AR, H0303192CR and H0212269KR were irradiated under the same conditions, namely 4 Mrad and 14 lb/tray. No significant changes were found compared to the mean of Experiment 2. The variation found appeared to be mainly from tray flatness rather than batch differences (see Table 15). At the same dosage, the viscosities of the three batches were 24-25 cP. Because of the apparent variance of 18-47 cP within the same batch (see Trial 2, Batch A, 4 Mrad, Table 12), it was difficult to decide how much of the difference was due to different batches and how much was due to sampling effects.

Table 15. Batch difference

batch number A (average) B C Viscosity ¹ Viscosity ² Viscosity ³ 403334   242223 373334

^1See Table 12.

^2See Table 12.

³ See Table 12.

While certain embodiments of the present invention have been described and/or illustrated above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The invention is therefore not limited to the particular embodiments described and/or illustrated, but is capable of numerous variations and modifications without departing from the scope of the appended claims.

Claims (9)

1, oil well crushing agent, described pressure break agent comprises:

A) propping agent; With

B) have the polygalactomannan of about 100,000 dalton to about 250,000 daltonian molecular weight.

2, the oil well crushing agent of claim 1, wherein polygalactomannan also has and is lower than about 3.0 polymolecularity and at least 90% hydration in 3 minutes.

3, the oil well crushing agent of claim 1, described pressure break agent also comprises additive.

4, the oil well crushing agent of claim 3, wherein this polygalactomannan also has and is lower than about 3.0 polymolecularity and at least 90% hydration in 3 minutes.

5, the oil well crushing agent of claim 3, wherein crosslinking additives is selected from boric acid ester, titanic acid ester or zirconate organo-metallic crosslinker.

6, the oil well crushing agent of claim 1, described pressure break agent also comprises crosslinking additives, and wherein the polymolecularity of polygalactomannan is lower than 3.0.

7, the oil well crushing agent of claim 1, described pressure break agent also comprises crosslinking additives, and wherein at least 90% polygalactomannan became hydrated product in 3 minutes.

8, polygalactomannan is depolymerized to the polygalactomannan of the method production of predetermined molecular weight, described method comprises allows polygalactomannan stand the radiating step of mainly being made up of electron beam.

9, the polygalactomannan of claim 8, wherein this polygalactomannan is selected from guar gum, the guar-bean lobe, hydroxypropylguar gum, cation guar gum, Viscogum BE, tara gum, carboxymethyl guar glue, Carboxymethyl hydroxypropyl guar, positively charged ion hydroxypropylguar gum, hydroxyalkyl guar gum and carboxyalkyl guar gum.

Images